Something to keep in mind about threat meters is that it requires that party mates also have the threat meter - they operate upon reading the abilities performed as stated in the combat log and assimilating the information for visual display to show players where they are in relation to other members of their party/raid group.
Omen is one of the most popular because it is also backwards compatible with the most commonly used threat meter used pre-BC (KTM Threat Meter). Omen also is updated regularly, be sure to check wowace frequently for a new version!
I find that as a healer, I am always recommending a unit frame mod. I used AG_unitframes for my party and switched to Grid (another wowace mod) when in a raid. Grid is one of the most powerful raid frames without taking away your ability to play the game. It tracks important things such as hot's, incoming heals, and aggro gained. I found the aggro warning upon raid members invaluable when healing a raid.
Other common mods include proximo for arenas, deadly boss mods for raiding, hawksy recap for a damage meter, simplechat for a chatmod and there are a slew of bar mods if it is your desire to move or change the display of your buttons. Personally, I use trinity.
Being sad is the same as giving up.